How to make a HTTP-get request in swift 3.1 using URLSession

[sohilpandya]

Ever wondered how you can communicate with a 3rd party from your iPhone app? Using HTTP requests of course! In this short tutorial, we'll be creating our very first request to a 3rd party API all inside of a Playground. 😄

The idea behind the HTTP-get request is to fetch information from the Game of Thrones API.

• let's start by creating a new Playground in XCode. http-request

• add the URL from which you want to fetch information from

// here we are initializing the URL Struct with the path which we want to access from the API
let url = URL(string: "http://anapioficeandfire.com/api/characters/583")!

• next, let's instantiate a shared URLSession which will provide us with an API to interact with 3rd parties (fetch/post data)

let urlSession = URLSession.shared

• create the URLRequest which will be used for fetching the data

let getRequest = URLRequest(url: url)

• create the task that you'd like to run with the completion handler and run the task

// we are going to call the `dataTask` method which will retrieve the content of a url based on a specific URL request object and calls the completionHandler.
// completion handler returns
// | data | URLResponse | error (if present) |
// | ---- | ---- | ---- |
// | data retruned by server | returned object from HTTP or HTTPS requests | Error object (either error or nil)
let task = urlSssion.dataTask(with: getRequest as URLRequest, completionHandler: { _, _, _ in })

// then call task.resume to fetch the results. 
task.resume()

• Lets update the completion handler so that it prints some data for us and to check if this works.

let task = urlSession.dataTask(with: getRequest as URLRequest, completionHandler: { data, response, error in

    guard error == nil else {
        return
    }
 
    guard let data = data else {
        return
    }
    
    do {

       // the data is returned in JSON format and needs to be converted into something that swift can work with
       // we are converting it into a dictionary of type [String: Any]
        if let json = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as? [String: Any] {
            print(json["name"]!)
            print(json["playedBy"]!)
            print(json["tvSeries"]!)
        }
    } catch let error {
        print(error.localizedDescription)
    }
})

task.resume()

• Finally, add this line to let this task run in playgrounds

PlaygroundPage.current.needsIndefiniteExecution = true

If you now run the playground, you should see the following information in the console

Jon Snow // String
(
    "Kit Harington" // Array
)
(
    "Season 1", // Array
    "Season 2",
    "Season 3",
    "Season 4",
    "Season 5",
    "Season 6"
)